Computer Tomograph (CT) imaging of mandibular anatomical substrate in animal model restored with nanostructured hydroxyapatite compounds.

INTRODUCTION
This study was meant to test a new type of bone graft on an animal model. This material was a nanostructured hydroxyapatite.


MATERIALS AND METHODS
the study was conducted according to Ethic Committee Regulation on animal model (Oryctolagus cuniculus - rabbit) between August and November 2014, at "Carol Davila" University of Medicine and Pharmacy, Bucharest. The animals were tested by using a CT at the level of the mandible before and after using the nanostructured hydroxyapatite.


RESULTS
The animals were CT scanned at 1, 2 and respectively 3 months, noticing a growth of the mandibular bone density. After 3 months, a bone density equal with the density of the healthy bone was noticed.


CONCLUSIONS
The use of the bone graft could be a viable alternative to available materials. The advantage was that bone recovery had a density similar to the density of the healthy bone and the cost of production was low because it was made out of Calcium azotate and monobasic ammonium phosphate.


Introduction
Bone graft materials are used in various orthopedic and maxillofacial surgery procedures for the treatment of bony defects caused by fractures, tumor resections or bone loss. In the last decades, different types of graft biomaterials with various origins have been developed, displaying specific advantages and disadvantages. In general, bone substitution materials can be categorized into natural bone grafts (autografts, allografts, xenografts, coralline) and synthetic bone grafts (alloplasts).
Hydroxyapatite is one of the materials frequently used in the reconstruction of dental bone defects.
This type of material is part of the category of biomaterials, which are classified as it follows [1][2][3][4][5]: A) Autografs -autologous or autogenous bone grafting involves the use of the bone obtained from the same individual receiving the graft. B) Allografts -Allograft is derived from humans. The difference is that the allograft is harvested from an individual other than the one receiving the graft [6][7][8]. C) Synthetic variants -Flexible hydrogel-hydroxyapatite (HA) composite which has a mineral. D) Xenograft -Xenogratfs are bone grafts from a species other than human, such as bovine, and are used as a calcified matrix [9]. E) Alloplastic grafts -Alloplastic grafts may be made from hydroxyapatite, a naturally occurring mineral (main mineral component of bone) [10]. F) Ceramic-based bone graft substitutes (calcium sulfate, bioactive glass, and calcium phosphate) [11]. G) Polymer-based bone graft substitutes [12].
Depending on their use, bone grafts are available in different forms: hydroxyapatite granules of animal origin, spongious blocks of natural bone, elastic lamella of the cortical bone and formable, collagen paste from animal bone, etc. [13].
Calcium phosphates are the most abundant inorganic constituents of the living beings hard tissue, which provide bone and teeth with hardness, density and mechanical stability. Hydroxyapatite (Ca 10 (PO 4 ) 6 (OH) 2 ) is the main calcium phosphate in these tissues and the crystal unit cell comprises two entities. Institute of N fter the chem tion ( Fig. 1).
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Results
Several CT image investigations were performed after the surgery by using the HeadSpi/ Fine sections 0.6-2.4 program.
The images were taken as it follows: 1) Topogram for choosing the segment of interest.
The following technical parameters were used ( Table 1) All the images were digitally reconstructed ( Table 2), by using tri and bi-dimensional, frontal and sagittal reconstructions (MPR Range/ MPR Range 1). The purpose of these investigations was to make a comparison before and after surgery at the level of mandible (area of major interest in this study). The comparison was based on the parameters which resulted after the CT measurements on 150 relevant images for the study. A densitometry study was rolled out on these images. The animals were investigated at 1, 2 and 3 months. The bone density was measured in the mandibular region at the level of the insertion of the nanostructured hydroxyapatite.
The results are presented in the Table 3.

Discussion
Bone density increased in time after the surgery and 3 months after the surgery it reached a density equal with the density of the healthy bone. The obtained results were similar in all animals in the experiment.
Although there was a large variety of biomaterials for bone reconstruction, this nanostructured hydroxyapatite could provide an excellent support for dental implants.

Conclusions
The use of nanotechnology in dentistry means the use of innovative materials, materials that are tested or are in the process of testing.
The conversion of nanostructured hydroxyapatite into a bone graft biomaterial presents multiple advantages not only from the medical point of view but also from the environmental and economic ones. The main advantage is the natural origin of the material to be created. Furthermore, nanostructured hydroxyapatite possesses excellent biocompatible and osteoconductive properties as well as mechanical and compressive strength similar with the human bone.
Following the results obtained, the nanostructured hydroxyapatite completes the range of bone graft biomaterials having a good biocompatibility and a low cost of production which could make it an accessible biomaterial.